As dynamic random access memory (DRAM) feature sizes shrink to 4× or below, plug contact resistance increases due to a decrease in the size of a capacitor contact. To address this issue, tungsten (W) is being explored as a replacement for polysilicon for capacitor contacts. One advantage of using tungsten as a contact material is that reduced contact resistance and increased device speed are achieved, and stringent higher cell capacitance requirements are met. When tungsten is used as the contact material, a liner formed from titanium/titanium nitride (Ti/TiN) is conventionally used to provide improved adhesion and lower resistance to the contact due to the formation of titanium silicide (TiSi2) with the underlying polysilicon. During fabrication of the plug contacts, the titanium/titanium nitride is used as the liner in an opening in a dielectric material. Following formation of the liner, tungsten is deposited in the opening, such as by using a chemical vapor deposition (CVD) process. A chemical-mechanical planarization (CMP) process is performed to remove excess tungsten from the substrate surface and to planarize the exposed surfaces of the tungsten and titanium/titanium nitride within the opening.
After the CMP process, the tungsten and titanium/titanium nitride are removed by a dry etch process or a wet etch process to completely isolate the tungsten to prevent shorting of the plug contacts. However, conventional dry etch processes have low selectivity between the tungsten and a silicon nitride (Si3N4) material, which is used as an etch stop in the fabrication of the capacitor and also prevents shorts. Therefore, when the tungsten material is removed by the dry etch process, all or a portion of the silicon nitride material is also removed. The thinning of this silicon nitride material has downstream process implications. Another disadvantage of conventional dry etch processes is that the titanium/titanium nitride material cannot be isotropically etched from sidewalls of the tungsten material and the top of the silicon nitride material, which leads to poor isolation of the tungsten plugs. Conventional wet etch solutions, such as those that contain ammonium hydroxide or hydrogen peroxide, have minimal selectivity between the tungsten material and the titanium/titanium nitride material. When utilizing the conventional wet etch solutions to remove the titanium/titanium nitride material, the tungsten material is also entirely removed. Regardless of the hydrogen peroxide concentration, aqueous solutions of hydrogen peroxide exhibit low etch rates of the tungsten material and titanium/titanium nitride material.
Wet etch solutions that include ozone are known in the art. Ozone-containing solutions have been used to etch a metal nitride material relative to silicon, silicon dioxide, silicon nitride, or doped silicon oxides. Ozone-containing solutions have also been used to remove contaminants from silicon wafers, such as to remove inorganic or organic residues and particles.
It would be desirable to be able to selectively remove metal nitride materials on semiconductor device structures having both metal and metal nitride materials.